Piezoelectric crystal assembly



Feb. 18, 1958 FlsHER ET AL 2,824,219

PIEZOELECTRIO CRYSTAL ASSEMBLY Filed Nov. 8, 1954 NV TOR. ee/1e I I United States Patent PIEZOELECTRIC CRYSTAL ASSENIBLY George F. Fisher, Parkville, and Howard E. Dillon,

Kansas City North, M0., assignors to Midland Manufacturing Co., Inc., Kansas City, Kans.

Application November 8, 1954, Serial No. 467,342

1 Claim. (Cl. 3109.4)

This invention relates generally to piezoelectric crys tal assemblies and, more particularly, to an improved assembly of such type possessing important advantages over prior assemblies from the standpoints of miniaturization, ruggedness, simplicity of assembly and manufacturing economy.

One of the most important objects of the invention is to provide a piezoelectric crystal assembly of substantially fiat, disc-like configuration whose dimensions have been minimized to present a miniaturized but rugged and operational eificient component adapted for mounting in electrical circuitry in substantially the same manner as is common with electrical condensers, resistors and the like.

Another important object of the invention is to provide such an assembly utilizing a metallic housing in surrounding relationship to the piezoelectric element so that the latter can be fully shielded by the grounding of such housing.

Another important object of the invention is to provide such a metallic housing for a piezoelectric element which has an opening conveniently disposed for depositing additional amounts of metal or the like upon the surface of the crystal element for final adjustment of the frequency of the latter after it has been assembled within the housing, together with closure means for quickly and conveniently sealing such opening after such final frequency adjustment has been completed.

Other important objects of the invention including important details of construction, will be made clear or become apparent as the following description of the assembly of this invention progresses.

In the accompanying drawing:

Figure 1 is a perspective view of a completed assembly made in accordance with the invention;

Fig. 2 is an exploded, perspective view of the principal, structural parts of the assembly after fabrication but before same have been assembled into a completed unit;

Fig. 3 is a top plan view of a completed unit made in accordance with the invention;

Fig. 4 is a top plan view of the unit in partially assembled condition with one of the sections of the housing not yet in place;

.Fig. 5 is a fragmentary cross sectional view taken on line VV of Fig. 3; and

Fig. 6 is a top plan view of a unit illustrating certain modifications contemplated by the invention.

Heretofore, piezoelectric crystal assemblies have characteristically been subject to one or more of the disadvantages of being heavy, bulky and space consuming or fragile in nature. This invention, accordingly, will be seen to evidence utility in overcoming all of such common disadvantages of conventional crystal assemblies. The combination of structure contemplated by this invention presentan assembly which may be handled, mounted and connected into electrical circuitry in a manner generally analogous to those prevailing in respect of other conventional types of small electrical components. Manifestly, this results, not only in savings from elimination of unnecessary parts, such as mounting sockets and the like as used with conventional crystal assemblies, but also in substantial savings in materials used for manufacture of the assembly itself and in the labor required for its mounting and connection in electrical apparatus.

Referring now to the accompanying drawing, the numeral 10 broadly designates a piezoelectric crystal assembly made in accordance with the invention and including a pair of opposed housing sections broadly designated 12 and 14, a pair of conductors broadly designated 16 and 18, a piezoelectric crystal element broadly designated 20, and certain other parts hereinafter more fully identified. Housing sections 12 and 14 are each essentially pan-like in character and are preferably formed of aluminum or some other strong but light and electrically conductive metal. Section 12 includes an outer, annular rim portion 22 from which is laterally offset at an angle an annular, frusto-conical portion 24 which, in turn, carries a circular, central portion 26 preferably having a circular indented portion 28 in which a substantially T-shaped out has been made to present an opening 36 and a complementary closure piece 32 for opening 36 which is integrally connected with indented portion 23 by a radially extending stub 34. At opposite edges of section 12, a pair of substantially semicylindrical, channel forming portions 36 and 38 are impressed in rim portion 22 and a part of frusto-conical portion 24, as most clearly illustrated in Fig. 2. Channel forming portions 36 and 38 are adapted to pass conductors 16 and 18 from the exterior of the sectioned housing 1214 to the interior thereof.

Housing section 14 includes an annular rim portion 40 of dimensions substantially the same as those of rim portion 22 of section 12, an annular flange or band portion 42 extending laterally from the circumferential edge of rim portion 40 in one direction, an annular, frustoconical portion 44 extending laterally from the inner edge of rim portion 40 at an angle in a directiton opposite to that to which band portion 42 extends from rim portion 40, and a circular, central portion 46 carried by frustoconical portion 44 and closing the same. It may be noted that central portion 26 of section 12 and central portion 46 of section 14 are preferably substantially flat in order that the overall housing 12-14 may have a fiat, disc-like configuration for conservation of mounting space. Section 14 is provided with a pair of channel forming portions 48 and Si essentially similar to portions 36 and 38 of section 12, except that portions 48 and 50 are stamped into band portion 42 of section 14 as well as rim portion 49 and frusto-conical portion 44 thereof. The manner in which the channels defined by portions 36, 38, 48 and 5t communicate with the cavities of sections 12 and 14, and therefore, the interior chamber defined by sections 12 and 14 when in assembled condition, will be particularly clear from Fig. 2.

Although various shapes of substantially flat, plate-like pieces of quartz or other piezoelectric material can be used as the crystal element 20 without departing from the invention (it being noted that the generally circular shape of sections 12 and 14 can even be altered to accommodate elements 20 of different shape, if desired), the preferred form of element 20 is illustrated and comprises a circular disc-like plate 52 of quartz cut from the mother crystal at an angle adapting the same for operation in a high frequency, thickness shear mode of vibration. ere again, although it is to be understood that the type of plate 52 described is currently deemed best adapted for accomplishment of the miniaturization objectives of the invention, other cuts of quartz or crystals of other materials could obviously be used with seine advantage being realized from the structural combination.

Plate 52 is provided with a pair of thin, metallic electrode coatings 5.4 and 56 respectively deposited on the opposite major faces of the element 20. As will be clear from the drawing, each of electrode coatings 54 and 56 includes a contacting strip portion 58 and 6.0 respectively, it being noted that strip 58 extends from the main body of electrode 56, which is centrally disposed upon its major face of element to one side of the circumferential edge of element 28, while strip 6%. extends from the main body of electrode 54 toward the opposite circumferential edge of element 28. The major faces of element 20 upon which electrode coatings 54 and 56 are disposed are respectively identified by the numeral 62 and 64 in Fig. 5.

Conductor 16 preferably includes a length 66 of tinned, reasonably flexible although resilient wire to one end of which is attached by soldering or the like as at 68, a

relatively shorter length 70 of highly resilient wire, such as Phosphor bronze, having a two-turn coil 72 formed therein. The adjacent turns of coil 72 are normally disposed in interengagement with each other and are, ac cordingly, adapted to frictionally grip element 26 when the latter is inserted therebetween, as most clearly indicated in Figs. 2 and 4. It will be understood that a portion of length 66 of conductor 16 extends into the channeling or passage formed by portion 36 of section 12 and portion 48 of section 14 when the sections 12 and 14 are in assembled condition. Length 74 of conductor 16 is, therefore, disposed substantially entirely within the interior chamber of sectioned housing 1214. Similarly, conductor 18 includes a length 74 and a length 76 reis rotated during this step to dispose portions 36 and 38 thereof in alignment with portions 48 and 50 of section 14 and, therefore, in engagement with sleeves 82 and 84 respectively. Presuming that fine adjustment of frequency may be desired after the element 20 has been mounted within housing 1214, the closure 32 will at this stage of assembly be left in the open condition illustrated in Fig. 2; With the sections 12 and 14 in the relationship described, the band portion 42 of section 14 is then crimped over rim portion 22 of section 12 as at 86, and portions 36 and 4 8 and portions 3.8 and 50 are respectively crimped about sleeves 82 and 84 to tightly hold the latter and provide a substantial seal for the housing 12 14 (neglecting for the moment the opening 30).

If no fine adjustment of the frequency of response of the element 20 is necessary, the closure 32 is then bent into co-planar relationship with portion 28 of section 12 nd the op nin 30 s ed y lderi or th l as spectively corresponding to lengths 66 and 70 of conductor 16 lengths 74 and 76 being joined by soldering or the like as at 78, and a coil 80 similar to coil 72 being provided upon length 76. Preferably, coils 72 and 80 are also bonded to element 20 after insertion of the latter by means of any suitable cementitious material, as indicated at 73 and 81. Conductor 18 is adapted to pass through the channeling of portions 38 and 50 in the same manner as described for conductor 16 with respect to channel forming portions 36 and 48.

Conductors 16 and 18 are respectively provided with cylindrical supporting sleeves 82 and 84, which are of electrical insulating, and preferably resilient material such as rubber, plastic or the like. As will be clear from the drawing, sleeve 82 is adapted to be received within channel forming portions 36 and 38 when section 12 is emplaced upon section 14 with rim portion 22 of the former within band portion 42 and in abutment with rim portion 40 of the latter. Similarly, sleeve 84, through which conductor 18 passes, is accommodated by channel forming portions 38 and 50. It is significant that portions 36 and 38 of section 12 are of dimension such that they fit within the part of corresponding portions 48 and 50 of section 14 which are formed from band portion 14 thereof.

Accordingly, the steps in assembling the unit 10 will obviously be understood to include insertion of the element 2 8 within coils 72 and 80 of conductors 16 and 18 respectively in such manner that strips 58 and 68 of electrodes 56 and 54 are in respective electrical contacting engagement with coils 72 and 80 of conductors 16 and 18, the emplacement of sleeves 82 and 84 upon conductors 16 and 18 respectively in the manner illustrated in Fig. 2, the emplacement of conductors 16 and 18, element 20 and sleeves 82 and 84 within section 14 in such manner that sleeves 82 and 84 are received by and extend slightly beyond portions 48 and 50 respectively of section 14,

in substantially the condition illustrated in Fig. 4. When the preceding steps have been completed, section 12 is emplaced upon section 14 with rim portion 22 of section 12 within band portion 42 of section 14 and in abutment with rim portion 40 of the latter. Manifestly, section 12 dicated at 88. If such final adjustment is desired, however, additional metal may conveniently be deposited upon face 62 of element 20 through the access afforded by openingfil) until the desired frequency of response for element 28 has been attained, as is well under stood in the art. Closure member 32 i then moved to its co-planar relationship with parts 28 and soldered as at 88, as above explained. When so assembled, the unit 10 meets all ordinary requirements relative to hermetical sealing. However, if further protection for the housing 1214 is desired, or if further protection against the ingress of moisture into the chamber of housing 1214 is desired, a coating of any suitable wax or other material, for instance Glyptal, may be coated upon the unit 10 including the portions of conductors 16 and 18 immediately adjacent housing 1214.

It will now be apparent that the overall unit 10 provides a piezoelectric component for use in electrical apparatus possessing many advantages over the bulky, expensive and inconvenient crystal mounting structures heretofore existing and conventionally used.

Reference is now made to Fig. 6 wherein are illustrated two important possible modifications of the basic structure above described. The first of these contemplates the possibility of length 74 of conductor 18 being soldered to the metallic body of housing 1214 as at to efiiect a shielding of element 20 by housing 12-414 where conductor 18 is to be grounded. Another modified construction which is useful in some applications, is the attachment of a lug or bracket 82 to housing 12 14 by soldering or the like as at 94, lug 92 preferably being provided with a perforation 86 for use in rigidly mounting the unit 10 to a chassis or the like (not shown). It may be further noted that lug 92 is preferably of a good conducting metal so that, by grounding the lug 92 in connection with its mounting, the housing 12 1.4 may thereby also be grounded for shielding purposes, even though the greunding connection 92 betweenhousing 1214 and conductor 18 may or may not also be utilized.

It will now be obvious to those skilled in the art that many minor modifications or changes might be made from the precise structure described without materially departing from the true spirit or intention of the invention. Accordingly, it is to be understood that the invention should be deemed limited only by the scope of the appended claim.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

A piezoelectric crystal assembly comprising a pair of opposed, generally circular, pan-like sections each having a cavity therein; means interconnecting the sections in opposed relationship to present a housing having a cham ber therewithin; a piezoelectric crystal element Within the chamber; a plurality of electrode coatings on the element; a conductor for each electrode coating respectively extending from the exterior of the housing into the chamber thereof; and structure for each of said conductors References Cited in the file of this patent UNITED STATES PATENTS Bush Apr. 16, 1929 Hawk Ian. 14, 1941 Lutzens Dec. 15, 1942 Sykes Jan. 8, 1946 La Brie Nov. 1, 1949 Reeves Nov. 22, 1949 Caroselli May 30, 1950 Wolfskill Apr. 14, 1953 Bujan Apr. 24, 1956 

